1. Field of the Invention
This invention relates to a corneal shape measuring apparatus which may be used to measure, for example, the shape of the cornea of a subject's eye before and after eye surgery.
2. Description of the Prior Art
In the prior art, it has been the practice to measure the shape of a subject's eye during eye surgery, and in particular during cataract operations. This measurement may be either qualitative or quantitative.
In the qualitative measurement, as shown for example in FIG. 11, an operator 1 places an indicator 2 between the objective lens (not shown) of a surgical microscope 3 and the eye 5 of a subject 4. An image of the indicator 2 is projected onto the cornea of the subject's eye 5 by illuminating light, and the extent of corneal deformation is qualitatively determined by observing the deformation of the image of the indicator 2 reflected by the cornea using the surgical microscope 3.
Alternatively in the quantitative measurement, as shown for example in FIG. 12, an indicator 6 is installed beneath a supporting member 3a of a surgical microscope 3 such that it can be freely inserted or withdrawn from beneath the objective lens (not shown) of the microscope 3, an image of the indicator 6 is projected onto the cornea of a subject's eye 5 by illuminating light. The image of the indicator 6 reflected by the cornea is detected by a photodetector (not shown), and the extent of corneal deformation is quantitatively determined by a computing circuit based on a signal received from this photodetector.
In the aforesaid qualitative corneal shape measuring device, as the operator 1 has to hold the indicator 2 with his hands, it is difficult to position the center axis of the indicator 2 to coincide with the optic axis 0 of the objective lens of the surgical microscope 3.
Further, if the center axis of this indicator 2 is inclined at an angle with respect to the optic axis 0 of the objective lens, the image of the indicator is projected onto the subject's eye at an angle so that the cornea of the eye may appear to be deformed even if it is not.
In the aforesaid quantitative corneal shape measuring apparatus, although the optic axis of the indicator 6 is not inclined with respect to the optic axis 0 of the objective lens as it is in the qualitative method, the indicator 6 is permanently installed underneath and close to the surgical microscope 3. There is, therefore, little space to perform the operation, and the indicator becomes a hindrance when carrying out surgical procedures.
In some cases, it may be required to perform corneal measurements not only close to the optic axis, but also up to the periphery of the subject's eye 5. It is then necessary to move the indicator 6 closer to the cornea to enlarge the projected image of the indicator.
In such a case, however, a mechanism is necessary to move the indicator 6 forward or backward along the optic axis. This is undesirable from a hygiene viewpoint and also makes the apparatus more complex.